It is frequently necessary to sample or remove a sample from a suspect tissue for testing. In humans, such a sample removal is particularly useful in the diagnosis and treatment of cancerous or pre-cancerous conditions. In the case of suspected cancer, particularly cancer of the breast, early detection and diagnosis is critical to the success of the patient's treatment and recovery.
Various techniques are available to aid in detection and diagnosis, including physical examination and imaging, such as mammography, x-ray, ultrasound, magnetic resonance imaging (MRI), and the like. When a condition is detected that suggests the possibility of cancer, a biopsy can be performed to obtain tissue samples for a complete diagnosis.
One biopsy technique frequently performed utilizes a cannula assembly comprising a stylet and a cannula that telescopically receives the stylet. One group of cannula assemblies is based on the combination of a notched inner stylet and an outer severing cannula. The stylet is retained within the lumen of the outer cannula such that the pointed end of the stylet closes off the open end of the cannula. The stylet and cannula are advanced into the tissue mass until they are near the desired biopsy site. The stylet is then advanced relative to the outer cannula to expose the notch to the biopsy site where the tissue prolapses into the notch. The outer cannula is then advanced to sever the tissue in the notch. Another group of cannula assemblies is based on a coring cannula in combination with a non-notched stylet. The stylet is used to plug the end of the coring cannula during the insertion of the coring cannula into the tissue adjacent the biopsy site. The coring cannula is then advanced relative to the stylet into the biopsy site to retain a sample within the coring cannula.
Many biopsy devices are provided with an actuator assembly for automating the firing of a cannula assembly. The actuator assembly can include springs that bias the cannula and stylet to the fired position. The cannula assembly must be cocked or armed prior to firing, which requires moving the cannula and stylet against the spring force. Some biopsy devices arm the cannula and stylet simultaneously. The disadvantage to this type of cocking operation is that the user must over come the spring force biasing both the cannula and stylet at once. Other biopsy devices arm the cannula and stylet sequentially. The advantage to this type of cocking operation is that biopsy device requires less effort to arm, since the user must only overcome the spring force biasing one of the cannula or the stylet at a time.